1. Field of the Invention
The invention relates to liquid crystal display (LCD) devices, and in particular to reflective LCD devices and fabrication methods thereof
2. Description of the Related Art
Liquid crystal display (LCD) devices have many advantages such as small volume, light weight and low power consumption, and are applicable in a variety of electronic and communication devices including notebook computers, personal digital assistants (PDA), mobile phones and the like due to lighter weight, thinner profile, and increased portability.
A conventional LCD device includes a pair of substrates with opposing electrodes thereon. A liquid crystal layer is interposed between the pair of substrates. An electric field is applied on the opposing electrodes to control liquid crystal molecular orientations in the liquid crystal layer, thereby displaying desirable images. Two alignment layers are separately interposed between the interfaces between the liquid crystal layer and each substrate, providing initial orientations and pre-tilt status for the molecules in the liquid crystal layer.
Conventional transflective LCD devices can take advantage of the ambient light and back light to display better quality of images. The transmissive mode can enhance the reflective mode in dark environments to improve brightness. The reflective mode can enhance the transmissive mode in bright environments for power conservation as well as overcoming the washout effect. The distance of light travel of the reflective region is twice as long as the distance of light travel of the transmissive region; however, the cell gap in the reflective region must differ from the cell gap in the transmissive region, resulting in deteriorating LCD performance, such as variations in brightness and color.
U.S. Pat. No. 6,862,058, the entirety of which is hereby incorporated by reference discloses a single gap transflective LCD device. In each pixel, different alignments layer are formed on the reflective region and the transmissive region respectively to reach the same phase retardation. A vertical alignment layer is formed on an active matrix substrate. A mask layer is disposed on the reflective region, thereby exposing the transmissive region under UV radiation. The vertical alignment on the transmissive region is transferred to a horizontal alignment layer. The mask layer is then removed. A rubbing procedure is performed on the vertical alignment layer on the reflective region, while a horizontal alignment layer is left on the transmissive region.
FIG. 1 is a cross section of a conventional transflective LCD device with different alignment layers on the reflective and the transmissive regions respectively. Referring to FIG. 1, a conventional transflective LCD device includes a lower substrate 11 such as an active matrix substrate and an upper substrate 21 such as a glass substrate with a color filter substrate 22 thereon. A liquid crystal layer 30 is interposed between the first substrate 11 and the second substrate 21. The transflective LCD device can be divided into a plurality of pixel regions. Each pixel region comprises a reflective region R and a transmissive region T. A transparent electrode 14 is formed on the lower substrate 11. A planarization layer 13 isolates the transparent electrode 14 from the lower substrate 11. The transparent electrode 14 electrically connects thin film transistors 12 from the lower substrate 11 via a contact hole 18. A reflector 15 is formed on the reflective region R of the transparent electrode 14. A vertical alignment layer 17 and a horizontal alignment layer 16 are respectively formed on the reflective region R and the transmissive region T of the lower substrate 11. A common electrode 23 is disposed on the color filter 22. A horizontal alignment layer 24 is formed on the common electrode 23. Different alignments are provided with respect to the reflective region R and the transmissive region T of the transflective LCD devices.
Forming different alignment layers on the reflective region R and the transmissive region T respectively, however, requires intricate lithography processes. For example, a polyimide (PI) alignment layer is selectively exposed on specific regions to induce photochemical reaction. The exposed regions of the PI alignment layer transits from vertical alignment to horizontal alignment, thereby achieving multi-domain alignments with different pre-tilt-angles. The conventional method requires the tedious addition of photo-catalyst in PI alignment layer and photo mask procedures, causing high production cost and low yield. It is desirable to overcome these and other problems of the prior art and to provide transflective LCD devices including T and R regions with different alignments that provide both regions with high light modulation efficiency.